1. FIELD OF THE INVENTION
The present invention relates to a process for producing tubular shaped fibrous articles.
2. STATEMENT OF THE PRIOR ART
Rod shaped fibrous articles used as a core for belt-tip pens*, filters, etc. have heretofore been prepared by cutting fulled felts of wool or felts of chemical fibers or synthetic fibers obtained by employing a binder or through mechanical entanglement, to predetermined shaped and sizes. (* felt-tip pens: the core, the end portion of which is felt-tip, is made from compact fibrous materials). Further, in the case of tobacco filters and the like, use has been made of a process comprising the steps of depositing triacetin onto crimped tows to plasticize it and shaping the resulting products into rods. Still further, in recent years, various shaped fibrous articles have been obtained with the use of hot-melt-adhesive composite fibers. For instance, U.S. Pat. No. 4,270,962 disclosed a process for producing rod-form shaped fibrous articles by heat treating a fibrous bundle containing at least 20% by weight of adhesive fibers by introducing the fibrous bundle into a heating zone through an elongated transport zone consisting of a single hollow pipe that is surrounded by said heating zone, imparting heat to the exterior portion of said fibrous bundle by directing heat against the exterior of said transport zone and imparting heat throughout the interior of said fibrous bundle by directing heated gas outwardly through the interior of said transport zone in a direction opposite to the inward movement of said fibrous bundle through said transport zone. With this process, however, it is possible to obtain solid rod-form shaped fibrous articles, but it is impossible to obtain hollow ones.
U.S. Pat. Nos. 4,100,009 and 4,197,156 specifications teach a method for producing a hollow-cylindrically shaped fibrous article stabilized by hot adhesion, which comprises passing a web of gathered fiber layer carried on a conveyor belt through a heating zone, heating said web in such a way that a lower-melting component of composite fiber contained in the lower part of said web contacting the conveyor belt is not in the molten state and a lower-melting component contained in the upper part of said web is in the molten state, while separating said web from the conveyor belt, winding up said web on a take-up rod or tube in such a way that the upper surface thereof occupies the inner side of the winding, while heating the web further, cooling the wound up article and drawing out the take-up rod or tube from the shaped product, and an apparatus for carrying out the same. However, this method provides only shaped articles which are hard as well as of larger diameter and thickness, and involves relatively complicated steps.